I. Field
The present invention relates to communication, and more particularly to techniques for detecting signaling transmitted sporadically in a wireless communication system.
II. Background
A wireless device (e.g., a cellular phone) in a wireless communication system may be designed to operate in one of several modes, such as “active” and “idle”, at any given moment. In the active mode, the wireless device can actively exchange data with one or more base stations in the system, e.g., for a voice or data call. In the idle mode, the wireless device may monitor a paging channel (PCH) for messages applicable to the device. Such messages may include page messages that alert the wireless device to the presence of an incoming call and overhead messages that carry system information and other information for the wireless device.
In the idle mode, the wireless device continues to consume power to sustain circuitry needed to monitor the signals transmitted by the base stations in the system. The wireless device may be portable and powered by an internal battery. Power consumption by the wireless device in the idle mode decreases the available battery power, which shortens the standby time between battery recharges and the talk time when a call is placed or received. Hence, it is highly desirable to minimize power consumption in the idle mode to increase battery life.
In one common technique for reducing power consumption in the idle mode, user-specific messages are sent on the paging channel to the wireless device at designated times, if at all. The paging channel may be divided into numbered frames. The wireless device may be assigned specific frames on which it may receive user-specific messages. With such a paging channel, the wireless device can enter discontinuous reception (DRX) operation whereby it periodically, rather than continuously, monitors the paging channel for messages. While in DRX operation, the wireless device wakes up from a “sleep” state prior to its assigned frame, enters an “awake” state and processes the paging channel for messages, and reverts back to the sleep state if additional communication is not required. The wireless device powers down as much circuitry as possible while in the sleep state to conserve battery power.
In another common technique for further reducing power consumption in the idle mode, a paging indicator channel (PICH) is used to indicate whether or not a page message may be sent on the paging channel for the wireless device. The PICH carries paging indicators that are transmitted as binary On/Off values and may be detected quickly. The wireless device is assigned a specific paging indicator prior to each assigned frame on the PCH. The wireless device detects the assigned paging indicator. If the paging indicator indicates that no message will be sent on the paging channel for the wireless device, then the device would not need to process the paging channel and may go to sleep immediately.
The wireless device typically needs to perform certain tasks after waking up from sleep in order to detect the assigned paging indicators. The clock within the wireless device may have drifted, the wireless device may have moved, and/or the channel conditions may have changed during sleep. The wireless device typically needs to reacquire the frequency and timing of the signals transmitted by the base stations and estimate the channel response. The wireless device typically wakes up for a predetermined warm-up period prior to the assigned paging indicator in order to perform the necessary tasks and get ready to detect the paging indicators. It is desirable to minimize the warm-up period in order to reduce battery power consumption and extend battery life.
There is therefore a need in the art for techniques to detect paging indicators in a manner to reduce battery power consumption.